Process for the manufacture of levo-ascorbic acid



Patented Nov. 14, 1939 UNITED STATES PATENT OFFICE PROCESS FOR THEMANUFACTURED! LEVO-ASCORBIG A011) Franz Elger, Basel, Switzerland,assignor to Hoffmann-La Roche Inc., Nutley, N. J a corporation of NewJersey 3 Claims.

This application is a division of my co-pending application, SerialNumber 84,010, filed June 6, 1936, Patent 2,129,317.

Thisinvention relates to, the preparation of levo-ascorbic acid from2-keto-levo-gulonic acid or its derivatives. 'It is known thatlevo-ascorbic acid can be obtained by the action of alkaline reagents on2-keto-levo-gulonic acid or its esters and subsequent treatment withacids or by warming an acid solution of 2-keto-1evo-gulonic acid or suchof its derivatives as are readily hydrolysable by acids.

It has now been found that it is particularly advantageous to carry outthe transformation of 2-keto-levo-gulonic acid or its esters to asoorbicacid salts with the alkali salts of weak acids in alcoholic solution.The salts which are obtained are then converted into free ascorbic acidby subsequent treatment with an acid reagent.

In this manner levo-ascorbic acid is readily obtained in good yield in apure state.

The following examples serve to illustrate the invention but theinvention is not limited thereto:

Example 1 20.8 parts by weight of 2-keto-levo-gulonicacid-methyl-esterare dissolved in 300 parts by weight of methyl alcohol and 8.2 parts byWeight of finely powdered sodium bicarbonate added. While stirring themixture thoroughly, it is gradually heated'in the water-bath to theboiling point of the methyl alcohol. At about 50 C. the evolution of thecarbon dioxide already sets in. After stirring for four hours it iscooled and the sodium salt of ascorbic acid which separates is suckedoff. There is a yield of 18.6 parts by weight of sodium ascorbate, whichis 94 per cent of the theoretical quantity. The quantities remaining inthe mother liquor can be obtained in form of ascorbic acid by extractionof the residue obtained after acidification and evaporation of themother liquor to dryness in vacuo with absolute alcohol. Alternately, ofcourse, the reaction mixture can be acidified with hydrochloric acid,the methyl alcohol distilled off in vacuo and the ascorbic acidextracted from the mixture of sodium chloride and ascorbic acid with asuitable solvent such as absolute alcohol.

Example 2 104 parts by weight of 2-keto-levo-gulonicacid-methyl-ester'and 45 parts by weight of anhydrous sodium acetate are dissolved in 700parts by weight of methanol. When the mixture is heated on a water-baththe separation of sodium ascorbate soon begins. After some time the rateof seperation slackens but a yield exceeding 90 per cent can be obtainedif the methanol is distilled off, carrying with it some of the acid,adding fresh methanol and continuing the heating. The working up isperformed as described in Example 1.

I claim:

1. In a process for the manufacture of levoascorbic acid the stepcomprising heating a compound of the formula wherein R. represents aradical selected from the group consisting of hydrogen and alkylradicals in the presence of an alkali of a weak acid in substantiallyanhydrous alcoholic solution.

2. In a process for the manufacture of levoascorbic acid the stepcomprising heating a 2- keto-levo-gulonic ester in the presence of analkali salt of weak acid in substantially anhydrous alcoholic solution.

3. In a process for the manufacture of levoascorbic acid the stepcomprising heating a 2-keto-levo-gulonic ester in the presence of sodiumbicarbonate in substantially anhydrous alcoholic solution.

FRANZ ELGER.

